1. Field of the Present Disclosure
The present disclosure relates to an image processing apparatus and an image forming apparatus.
2. Description of the Related Art
In general, if there is a difference between a color range of image data and a color space of an outputting device that outputs an image based on the image data, a color value of the image data is converted to a color value within the color space of the outputting device.
An image processing apparatus (here referred as the first image processing apparatus) prepares a discrimination ellipse which has a reference color at the center thereof and passes through control colors that indicate a boundary obtained by a predetermined subjective evaluation in the L*a*b* coordinate system, and derives a color difference between the reference color and a reproduced color using a weight coefficient based on (a) a parameter of the prepared ellipse and (b) a hue difference between the reference color and the reproduced color.
When color tone of an image is changed in accordance with a user operation, another image processing apparatus (here referred as the second image processing apparatus) specifies a color difference of an objective color in the image, and determines available ranges of color property values (brightness, chroma, and hue) based on CIE1994 color difference formula corresponding to the specified color difference.
Further, another image processing apparatus corrects hue of a foreground of an image on the basis of hue of a background of the image.
In the aforementioned first image processing apparatus, it is required to identify the control colors using the subjective evaluation for all available reference colors (i.e. for all available objective colors of color conversion) in a color range or a color reproduction space of image data, and therefore a large number of reference colors results in much working burden for the subjective evaluation, and consequently it is not realistic. Further, it is not realistic due to complicated calculation for preparing the discrimination ellipse.
In the aforementioned second image processing apparatus, a user specifies the color property values (brightness, chroma, and hue), and therefore it does not perform automatic conversion to a proper color of a predetermined outputting device. Further, in this apparatus, a color difference specified by a user may exceed an allowed color difference.